[CAP_NET_ADMIN]

Why would you do 50k+ connections if they can't be active all at once either way? Unless you have 50k+ cores and IO beefy enough not to get overwhelmed due to that.

You can have as much connections as you want, but you'll have to trade it for having lower work mem numbers, which hurts performance. Traditional advice is to keep it below 500 per PostgreSQL instance (I'd say physical host).

I've ran dozens of micro services handling thousands of requests per second with a total connection limit of around 200 of which most was still unused - all without any server-side pooler.

[samlambert]

because people run large amounts of front ends and workers that create a significant amount of connections. it doesn't matter if they are all active.

[throwaway313373]

Why would you want every "frontend" keep an open connection all the time?

> it doesn't matter if they are all active

It does, if the connection is inactive (doesn't hold an open transaction) you should close it or return it to the pool.

[samlambert]

so you are suggesting you close a connection between queries?

[throwaway313373]

Between queries in the same transaction? No

Between transactions? Yes, absolutely

In fact, many libraries do it automatically.

For example, SQLAlchemy doc explicitly says [0]:

> After the commit, the Connection object associated with that transaction is closed, causing its underlying DBAPI connection to be released back to the connection pool associated with the Engine to which the Session is bound.

I expect other reasonably sane libs for working with transactional databases do the same.

So, if you are doing pooling correctly, you can only run out of available connections if you want to have a lot of long running transactions.

So, why would you want every of your 50k frontends keep an open transaction simultaneously?

[0] https://docs.sqlalchemy.org/en/20/orm/session_basics.html#co...

[nrdvana]

Because there's an overhead to make a connection, authenticate, set the default parameters on the connection, etc. I've never seen a framework that closed db connections between requests.

Of course, the better design is to write a nonblocking worker that can run async requests on a single connection, and not need a giant pool of blocking workers, but that is a major architecture plan that can't be added late in a project that started as blocking worker pools. MySQL has always fit well with those large blocking worker pools. Postgres less so.

[throwaway313373]

As I said, you can return the connection to the connection pool.

From the perspective of keeping the number of open connections low it doesn't really matter if you close it or return to the pool, because in either case the connection becomes available to other clients.